用threadLocal管理 session

package util;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateSessionFactory {
 private static final SessionFactory sessionFactory;
 //使用ThreadLocal管理Session
 private static final ThreadLocal threadLocal = new ThreadLocal();
 static {
  try {
   //根据hibernate.cfg.xml建立SessionFactory
   sessionFactory = new Configuration().configure().buildSessionFactory();
  } catch (Throwable ex) {
   ex.printStackTrace();
   System.err.println("建立SessionFactory错误" + ex);
   throw new ExceptionInInitializerError(ex);
  }
 }
  
    public static Session getSession() throws HibernateException {
  Session session = (Session) threadLocal.get();
  if (session == null || !session.isOpen()) {
   session = (sessionFactory != null) ? sessionFactory.openSession(): null;
   threadLocal.set(session);
  }
  return session;
 }
   
    public static SessionFactory getSessionFactory() {
  return sessionFactory;
 }
   
    public static void closeSession() throws HibernateException {
        Session session = (Session) threadLocal.get();
        threadLocal.set(null);

        if (session != null) {
            session.close();
        }
    }
}